1. Field of the Invention
The present invention relates to an electrophotographic photosensitive member, and more particularly to an electrophotographic photosensitive member having a photosensitive layer containing an azo pigment with a specific structure.
2. Related Background Art
Organic photoconductive materials used in electrophotographic photosensitive members are hitherto known to include photoconductive polymers as typified by poly-N-vinyl carbazole or low-molecular weight organic photoconductive materials such as 2,5-bis(p-diethylaminophenyl)-1,3,4-oxadiazole, and also those comprising a combination of such organic photoconductive material with various sorts of dyes or pigments.
The electrophotographic photosensitive members employing the organic photoconductive materials have the advantages that they can achieve a very high productivity and are inexpensive. They also have the advantages such that the color-sensitivity can be arbitrarily controlled by selecting sensitizers such as dyes or pigments to be used, and thus have been hitherto studied over a wide range. Particularly in recent years, a functionally separated photosensitive member comprising a charge generation layer comprised of an organic photoconductive dye or pigment, laminated with a charge transport layer comprised of the above photoconductive polymer or low molecular organic photoconductive material, has been developed to bring about remarkable improvement in the sensitivity and durability in which the conventional organic electrophotographic photosensitive members have been regarded as defective.
Among the organic photoconductive materials, many of azo pigments are commonly capable of showing superior photoconductivity. Moreover, pigment compounds with a variety of properties can be relatively readily obtained since the properties of pigments can be controlled depending on the manner by which an azo component and a coupler component are combined. Thus, a large number of pigments have been hitherto proposed.
As couplers used in such azo pigments, the Naphthol AS compounds as disclosed in Japanese Patent Application Laid-open No. 47-375438, etc., the benzcarbazole compounds as disclosed in Japanese Patent Application Laid-open No. 53-95033, etc., the naphthalimide compounds as disclosed in Japanese Patent Application Laid-open No. 54-79632, and the perylene compounds as disclosed in Japanese Patent Application Laid-open No. 57-176055 are already known in the art.
The electrophotographic photosensitive members that use conventional azo pigments, however, can not necessarily be said to be satisfactory in view of sensitivity, or potential stability when repeatedly used, and only a few materials have been put into practical use.